We have a SP13 Publishing site collection using Windows Authentication for DOMAIN-A and FBA/LDAP to DOMAIN-B. Everything looks good, People Picker, granting permissions to users of either domain, etc. The issue occurs when we apply a permission based on a group in DOMAIN-B. If we break inheritance on a folder, grant DOMAIN-B\reps permissions, a user in the DOMAIN-B\reps group receives "Sorry, this list has not been shared with you" message. If instead of granting permissions to DOMAIN-B\reps, we grant the permission to DOMAIN-B\usera, it works as expected.
It seems like SharePoint cannot get the members of DOMAIN-B\reps group. The Event Log has nothing, and looking at the ULS logs, it looks like nothing's wrong, it's simply logging access denied type messages. Any ideas what could be wrong or how to troubleshoot? Thanks!